Adding with Whole Tens

This is a complete lesson for 1st or 2nd grade about adding a two-digit number and a multiple of ten, such as 58 + 30. Students first use a visual model for tens and ones to add. Then the lesson explains a strategy for doing such sums: break the 2-digit number into parts before adding. The lesson has many exercises, word problems, a pattern exercise, and a fun puzzle.

1. The numbers are
shown with ten-sticks and one-dots. Write the sums.

+

a.

54

+

10

=

______

+

b.

______

+

20

=

______

+

c.

______

+

______

=

______

+

d.

______

+

______

=

______

+

e.

______

+

______

=

______

+

f.

______

+

______

=

______

Adding whole tens and
another
2-digit
number

Break down the other
number into tens and ones.
Add the tens. Then, add the ones.

2. Add.
Break the second number into tens and ones first. Then add the tens.

a. 10 + 34 =
_______

(10 + 30 + 4)

b.
10 + 28 = _______

(10 + _____ +
_____ )

c. 20 + 24 = _______

(20 + _____ + _____ )

d.
30 + 21 = _______

e. 50 + 17 = _______

f. 40 + 33 = _______

g.
60 + 23 = _______

h. 30 + 37 = _______

i. 70 + 25 = _______

3. Add. Break the first number into tens and ones first. Then add the tens.

a.
45 + 20 = _______

(40
+ 5 + 20)

b.
27 + 20 = _______

( _____ + _____ +
20 )

c.
45 + 40 = _______

( _____ + _____ +
40)

d. 46 + 30 = _______

e. 16 + 50 = _______

f. 38 + 60 = _______

g. 20 + 77 = _______

h.
58 + 40 = _______

i.
40 + 39 = _______

4. Explain in your own words how you can mentally add 21 + 60.

5.
Fill in the chart of doubles again,
and notice its PATTERN.

5 + 5 = _______

10 + 10 = _______

15 + 15 = _______

20 + 20 = _______

25 + 25 = _______

30 + 30 = _______

35 + 35 = _______

40 + 40 = _______

45 + 45 = _______

50 + 50 = _______

6. Isabella got 30
books out of the library, and read half of them in two
days. How many books does she have left to read?

7. Gwen and Mom went
shopping. They bought shoes for $40, a top for $10,
and a skirt for $20.
Mom paid half of the cost and Gwen paid the rest.
How much did
Gwen pay?

8. Jacob had $61. Then
he bought a toy for $30. How much money does he have
left?

9. Fill
in the missing numbers and find how many tens were
added.

a.
12 + _____ = 22

12 + _____ = 52

12 + _____ = 42

b.
45 + _____ = 65

45 + _____ = 55

45 + _____ = 75

c. 23 + _____ = 63

23 + _____ = 53

23 + _____ = 93

10. Add 10,
20, 30, or 40. In the box below the number, write “E” if the number is even,
and “O”, if the number is odd. What
do you notice?

+ 10

12

22

E

E

+ 20

19

O

+ 30

32

+ 40

37

+ 40

23

+ 30

58

+ 20

7

+ 10

85

How many different solutions can you find for this puzzle?
Find at least two. All numbers are whole tens.

How to set up algebraic equations to match word problems
Students often have problems setting up an equation for a word problem in algebra. To do that, they need to see the RELATIONSHIP between the different quantities in the problem. This article explains some of those relationships.